Process for preparing aspartates

ABSTRACT

The present invention relates to novel aspartates, their method of produciotn and the use of these mono and polyaspartates as reactive components for polyisocyanates in two-component polyurethane coating compositions and for preparing polyurethane prepolymers.

BACKGROUND OF THE INVENTION

The present invention relates to novel aspartates, a process forpreparing them from primary amines and maleates and to their use asreactive components for polyisocyanates in two-component polyurethanecoating compositions and for preparing polyurethane prepolymers.

Two-component coating compositions which contain, as binder, apolyisocyanate component combined with one or more isocyanate-reactivecomponents are known. They are suitable for preparing high qualitycoatings which are hard, elastic, abrasion resistant, solvent resistantand weather resistant.

Secondary polyamines which contain ester groups have become establishedin the two-component surface coating industry. They are particularlysuitable, in combination with lacquer polyisocyanates, as binders inlow-solvent or solvent-free, high solids coating compositions becausethey provide rapid curing of the coatings at low temperatures.

These secondary polyamines are polyaspartates and are described, e.g.,in U.S. Pat. Nos. 5,126,170, 5,214,086, 5,236,741, 5,243,012, 5,364,955,5,412,056, 5,623,045, 5,736,604, 6,183,870, 6,355,829, 6,458,293 and6,482,333 and published European patent application 667,362. Inaddition, aspartates containing aldimine groups are also known (see U.S.Pat. Nos. 5,489,704, 5,559,204 and 5,847,195). Their use as the onlyisocyanate-reactive component or mixed with other isocyanate-reactivecomponents in two-component coating compositions are also described inthe above-identified patents.

The process for preparing these polyaspartates is the reaction of thecorresponding primary polyamines with maleates or fumaratescorresponding to the formulaR₃OOC—C(R₁)═C(R₂)—COOR₄wherein R₁, R₂, R₃ and R₄ are identical or different organic groups,resulting in the formation of secondary polyamines. Due to stearic,structural and electronic effects, these secondary amino groups havesufficiently reduced reactivity towards isocyanate groups to be mixablewith polyisocyanates in a reliable and easy manner.

The reaction which is used to prepare polyaspartates is the addition ofprimary amines to the activated C—C double bond in vinyl carbonylcompounds, which has been described in the literature (see Chem. Ber.1946, 38, 83; Houben Weyl, Meth. d. Org. Chemie, vol.11/1, 272 (1957);Usp. Chimii 1969, 38, 1933). It has been found, however, that thisreaction does not proceed to completion during the course of the actualsynthesis process (e.g., 24 hours with stirring at 60° C.). The actualextent of the reaction is dependent upon the type of primary polyamine.Thus, the degree of conversion (measured by the concentration of free,unconverted maleate and fumarate, into which maleate rearranges in thepresence of basic catalysts) after 1 day with 1,6-hexanediamine is about90 to 93%. The degree of conversion after 1 day with a cycloaliphaticpolyamine having sterically hindered primary amino groups, i.e.,4,4′-diamino-3,3′-dimethyldicyclohexylmethane is only 77%. Complete oressentially complete conversion is achieved only after several days or,in the case of 4,4′-diamino-3,3′-dimethyldicyclohexyl-methane, onlyafter several months.

In a typical commecial production, the reaction is run for sixteen hourswhen the conversion is somewhere between 75 and 95% complete dependingon the amine used. The “unfinished” material is drummed and held instorage until the reaciton is complete. This typically takes anywherefrom two weeks to six months.

U.S. Pat. No. 5,821,326 describes the use of certain five-memberedaromatic ring compounds as catalyst to accelrate the preparation of theaspartates.

DESCRIPTION OF THE INVENTION

The present invention is directed to novel aspartates of the formula:

where

-   -   X represents an m-valent organic residue obtained by removing        the primary amino group or groups from a mono or polyamine which        has (cyclo)aliphatically bound amino groups and a number average        molecular weight of 60 to 6000, and which may contain further        functional groups that either are reactive with isocyanate        groups or are inert to isocyanate groups at temperatures of up        to 100° C.,    -   R₁ and R₂ may be identical or different and represent hydrogen        or organic groups which are inert towards isocyanate groups at a        temperature of 100° C. or less (both are preferably hydrogen),    -   R₃ and R₄ may be identical or different and represent organic        groups which are inert towards isocyanate groups at a        temperature of 100° C. or less (preferably a C₁ to C₈ and most        preferably methyl or ethyl),    -   R₅ represents hydrogen or together with R_(5′) and the carbon        atoms to which they are connected forms a six-membered        cycloalkyl group, with said cycloalkyl group being substituted        with from 0 to 3 alkyl groups having from 1 to 3 carbon atoms,    -   R_(5′) represents a moiety selected from the group consisting        of i) C₁ to C₈ alkyl groups which may be interrupted with an        oxygen atom, ii) C₆ to C₁₀ aryl groups, which may be substituted        with up to three alkyl groups having from 1 to 3 carbon atoms        and iii) C₆ to C₁₂ cycloalkyl groups, which may be substituted        with up to three alkyl groups having from 1 to 3 carbon atoms,    -   R₆ represents hydrogen or together with R_(6′) and the carbon        atoms to which they are connected forms a six-membered        cycloalkyl group, with said cycloalkyl group being substituted        with from 0 to 3 alkyl groups having from 1 to 3 carbon atoms,    -   R_(6′) represents a moiety selected from the group consisting        of i) C₁ to C₈ alkyl groups which may be interrupted with an        oxygen atom, ii) C₆ to C₁₀ aryl groups, which may be substituted        with up to three alkyl groups having from 1 to 3 carbon atoms        and iii) C₆ to C₁₂ cycloalkyl groups, which may be substituted        with up to three alkyl groups having from 1 to 3 carbon atoms,    -   with the proviso that R₅ and R₆ are the same and R_(5′) and        R_(6′) are the same, and    -   a and b represent integers of from 1 to 5, provided that the sum        of a and b is from 2 to 6.

The present invention also relates to a process for preparing aspartatesof the above formula comprising

-   -   A) reacting at a temperature of 0 to 100° C., in solution or in        the absence of a solvent and at an equivalent ratio of primary        amino groups in component a) to C═C double bonds in component b)        of from about 1.1:1 to about 3.0:1        -   a) mono or polyamines corresponding to formula (II)            X[—NH₂]_(m)   (II)        -    with        -   b) compounds corresponding to formula (III)            R₃OOC—C(R₁)═C(R₂)—COOR₄   (III)    -    wherein        -   X, R₁, R₂, R₃ and R₄ are as defined above and        -   m represents an integer of from 2 to 6, and    -   B) reacting the resultant product with an oxirane compound        selected from the group consisting of alkylene oxides,        cycloalkylene oxides, styrene oxide and glycidyl ethers.

The present invention also relates to a two-component coatingcomposition which contains, as binder,

-   -   a) a polyisocyanate component and    -   b) an isocyanate-reactive component containing        -   b1) a compound corresponding to formula (I) and        -   b2) optionally other isocyanate-reactive compounds,            wherein the equivalent ratio of isocyanate groups to            isocyanate-reactive groups is from about 0.8:1 to about 2:1,            and optionally, additives known in surface coatings            technology.

Finally, the present invention also relates to prepolymers containingurea, urethane, allophanate and/or biuret structures, which are based onthe reaction product of polyisocyanates with the aspartates of theinvention, optionally in admixture with one or more isocyanate-reactivecomponents.

The polyamines useful herein include i) high molecular weight amineshaving molecular weights of 400 to about 10,000, preferably 800 to about6,000, and ii) low molecular weight amines having molecular weightsbelow 400. The molecular weights are number average molecular weights(M_(n)) and are determined by end group analysis (NH number). Examplesof these polyamines are those wherein the amino groups are attached toaliphatic, cycloaliphatic, araliphatic and/or aromatic carbon atoms.

Suitable low molecular polyamine starting compounds include ethylenediamine, 1,2- and 1,3-propane diamine, 2-methyl-1,2-propane diamine,2,2-dimethyl-1,3-propane diamine, 1,3- and 1,4-butane diamine, 1,3- and1,5-pentane diamine, 2-methyl-1,5-pentane diamine, 1,6-hexane diamine,2,5-dimethyl-2,5-hexane diamine, 2,2,4- and/or2,4,4-trimethyl-1,6-hexane diamine, 1,7-heptane diamine, 1,8-octanediamine, 1,9-nonane diamine, 1,10-decane diamine, 1,11-undecane diamine,1,12-dodecane diamine, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, 2,4- and/or 2,6-hexahydrotoluylene diamine, 2,4′- and/or4,4′-diamino-dicyclohexylmethane, 3,3′-dialkyl-4,4′-diamino-dicyclohexylmethanes (such as 3,3′-dimethyl-4,4′-diamino-dicyclohexyl methane and3,3′-diethyl-4,4′-diamino-dicyclohexyl methane), 1,3- and/or1,4-cyclohexane diamine, 1,3-bis(methylamino)-cyclohexane,1,8-p-menthane diamine, hydrazine, hydrazides of semicarbazidocarboxylic acids, bis-hydrazides, bis-semicarbazides, phenylene diamine,2,4- and 2,6-toluylene diamine, 2,3- and 3,4-toluylene diamine, 2,4′-and/or 4,4′-diaminodiphenyl methane, higher functional polyphenylenepolymethylene polyamines obtained by the aniline/formaldehydecondensation reaction, N,N,N-tris-(2-aminoethyl)-amine, guanidine,melamine, N-(2-aminoethyl)-1,3-propane diamine, 3,3′-diamino-benzidine,polyoxypropylene amines, polyoxy-ethylene amines,2,4-bis-(4′-aminobenzyl)-aniline and mixtures thereof.

Preferred polyamines are1-amino-3-aminomethyl-3,5,5-trimethyl-cyclohexane (isophorone diamine orIPDA), bis-(4-aminocyclo-hexyl)-methane,bis-(4-amino-3-methylcyclohexyl)-methane, 1,6-diamino-hexane, 2-methylpentamethylene diamine and ethylene diamine.

Suitable high molecular weight polyamines correspond to the polyhydroxylcompounds used to prepare the NCO prepolymers with the exception thatthe terminal hydroxy groups are converted to amino groups, either byamination or by reacting the hydroxy groups with a diisocyanate andsubsequently hydrolyzing the terminal isocyanate group to an aminogroup. Preferred high molecular weight polyamines are amine-terminatedpolyethers such as the Jeffamine resins available from Huntsman.

Suitable optionally substituted maleic or fumaric acid esters for use inthe preparation of the aspartates are those corresponding to the formulaR₃OOC—C(R₁)═C(R₂)—COOR₄wherein R₁, R₂, R₃ and R₄ are as previously defined. Examples includethe dimethyl, diethyl, di-n-butyl and mixed alkyl esters of maleic acidand fumaric acid and the corresponding maleic or fumaric acid esterssubstituted by methyl in the 2- and/or 3-position. Suitable maleates orfumarates for preparing the aspartates of the present invention includedimethyl, diethyl, di-n-propyl, di-isopropyl, di-n-butyl anddi-2-ethylhexyl maleates, methylethylmaleate or the correspondingfumarates.

The aspartates of the present invention are prepared by first reactingcomponent a) with component b) at temperatures of 0 and 100° C.,preferably 20 to 80° C. and more preferably 20 to 60° C. wherein (i) theequivalent ratio of primary amino groups in component a) to C═C doublebond equivalents in component b) is from about 1.1:1 to about 3.0:1,preferably from about 1.1:1 to about 2.0:1. The reaction time may varyfrom about 1 to about 4 hours, depending upon the type of polyamine andthe desired maximum residual concentration of reactants in the reactionmixture. The resultant product is then reacted with an oxirane compoundselected from the group consisting of alkylene oxides, cycloalkyleneoxides, and phenylglycidyl ether. Specific useful oxirane compoundsinclude ethylene oxide, propylene oxide, butylene oxide, cyclohexeneoxide, phenyl gycidyl ether, butyl glycidyl ether, styrene oxide and thelike. This second reaction is typically conducted at a temperature offrom about 50 to about 100° C., for times ranging from about 1 to about4 hours. The ratio of reactants is chosen so that one mole of oxirane ispresent for each unreacted amine group.

The process to prepare the aspartates of the present invention may beeither be performed in solution or in the absence of a solvent. Solventmay also be added after the synthesis process, for example, to lower theviscosity. Suitable solvents include any organic solvents, preferablythose known from surface coating technology. Examples include acetone,methyl ethyl ketone, methyl isobutyl ketone, n-butyl acetate,methoxy-propyl acetate, toluene, xylene and higher aromatic solvents(such as the Solvesso solvents form Exxon).

The aspartates prepared according to the invention may be directly usedas reactive components for polyisocyanates after concluding thesynthesis process.

One use of the aspartates of the present invention is to preparecoatings from two-component coating compositions containing, as binder,

-   -   a) a polyisocyanate component and    -   b) an isocyanate-reactive component containing        -   b1) the aspartates of the invention and        -   b2) optionally other known isocyanate-reactive components.

Suitable polyisocyanate components a) are known and include thepolyisocyanates known from polyurethane chemistry, e.g, low molecularweight polyisocyanates and lacquer polyisocyanates prepared from theselow molecular weight polyisocyanates. Preferred are the lacquerpolyisocyanates, which are known from surface coating technology. Theselacquer polyisocyanates contain biuret groups, isocyanurate groups,allophanate groups, uretdione groups, carbodiimide groups and/orurethane groups and are preferably prepared from (cyclo)aliphaticpolyisocyanates.

Suitable low molecular weight polyisocyanates for use in accordance withthe present invention or for preparing the lacquer polyisocyanates arethose having a molecular weight of 140 to 300, such as1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI),2,2,4- and/or 2,4,4-trimethyl-hexamethylene diisocyanate,dodecamethylene diisocyanate, 2-methyl-1,5-diisocyanatopentane,1,4-diisocyanatocyclohexane,1-isocyanato-3,3,5-trimethyl-5-isocyanato-methylcyclohexane (IPDI), 2,4-and/or 4,4′ diisocyanato-dicyclohexyl-methane,1-isocyanato-1-methyl-3(4)-isocyanatomethyl-cyclohexane (IMCI), 2,4-and/or 2,6-hexahydrotoluylene diisocyanate (H₆TDI), 2,4- and/or4,4′-diisocyanatodiphenylmethane or mixtures of these isomers with theirhigher homologs (which may be obtained in known manner by thephosgenation of aniline/ formaldehyde condensates), 2,4- and/or2,6-diisocyanatotoluene, and mixtures thereof. The use of low molecularweight polyisocyanates themselves is not preferred. Also lacquerpolyisocyanates prepared from aromatic polyisocyanates, such as 2,4-and/or 2,6-diisocyanatotoluene, are also less preferred. The lacquerpolyisocyanates containing urethane groups are preferably based on lowmolecular weight polyhydroxyl compounds having molecular weights of 62to 300, such as ethylene glycol, propylene glycol and/ortrimethylol-propane.

Preferred lacquer polyisocyanates for use as component a) are thosebased on 1,6-hexamethylene diisocyanate and having an NCO content of 16to 24 wt. % and a maximum viscosity at 23° C. of 10,000, preferably 3000mPa.s.

Component b1) is selected from the aspartates of the present invention.Preferably, X represents a divalent hydrocarbon group obtained byremoving the amino groups from1-amino-3,3,5-trimethyl-5-aminomethyl-cyclohexane (IPDA),4,4′-diaminocyclohexylmethane (HMDAI),3,3′-dimethyl-4,4′-diaminodicyclohexylmethane (Lasomin C260, BASF),hexahydro-2,4- and/or 2,6-diaminotoluene (H₆TDA), isomers ofC-monomethyl-diaminodicyclohexyl-methanes,3(4)-aminomethyl-1-methylyclohexylamine (AMCA), hexane diamine (HDA) or2-methyl-5-pentanediamine.

Particularly preferred starting components b1) include those aspartatesin which R₃ and R₄ represent C₁ to C₈ alkyl groups such as methyl,ethyl, n-propyl, isopropyl, n-butyl or 2-ethylhexyl.

Optional starting components b2) are known compounds containing at leasttwo isocyanate-reactive groups, including groups which react withisocyanate groups under the effect of either moisture or/and heat.Examples include hydroxy-functional polyacrylates and polyesterpolyolsMixtures of these compounds may also be used.

In the binders used according to the invention, the amounts ofcomponents a), b1) and (optionally) b2) are selected such that theequivalent ratio isocyanate groups to isocyanate-reactive groups is fromabout 0.8:1 to about 2.0:1, and preferably from about 0.8:1 to about1.2:1.

The binders according to the invention are prepared by mixing theindividual components either in the absence of a solvent or in thepresence of the solvents which are conventionally used in polyurethanesurface coating technology. Suitable solvents include ethyl acetate,butyl acetate, methoxypropyl acetate, methyl isobutyl ketone, methylethyl ketone, xylene, N-methylpyrrolidone, petroleum spirit,chlorobenzene, Solvesso solvent or mixtures thereof.

Preferably, the ratio by weight binder components a) and b) to solventin the coating compositions according to the invention is from about40:60 to about 100:0, more preferably from about 60:40 to about 90:10.

The coating compositions may also contain the known additives fromsurface coating technology. These include pigments, fillers, flowcontrol agents, catalysts and anti-settling agents.

The properties of the coatings obtained from the coating compositionsaccording to the invention may be adjusted by appropriate selection ofthe type and ratios of starting components a), b1) and b2).

The coating compositions may be applied to any substrate in a singlelayer or in several layers by known methods, e.g., by spraying,painting, immersing, flooding or by using rollers or spreaders. Thecoating compositions according to the invention are suitable forpreparing coatings on substrates, such as metals, plastics, wood orglass. The coating compositions are especially suitable for coatingsteel sheeting, which is used for the production of vehicle bodies,machines, cladding panels, barrels and containers. The substrates may beprovided with suitable primer coats prior to applying the coatingcompositions according to the invention. Drying of the coatings may takeplace at a temperature of about 0 to 160° C.

The process for producing coatings using the aspartates of the presentinvention may also be used for the production of prepolymers containingurea, urethane, allophanate and/or biuret structures.

The aspartates of the present invention may be directly used aftercompletion of the synthesis process because, in contrast to prior artaspartates, an approximately complete degree of conversion is achieved.As a result of the low concentration of maleates, fumarates and primaryamino groups, these products are not only toxicologically andphysiologically harmless, they also exhibit a reasonable, as opposed toa vigorous, reactivity towards isocyanates. Due to their low viscosity,they are a more than suitable alternative, as reactive diluents, to theenvironmentally polluting organic solvents previously used and maytherefore be used in high quality, low-solvent or even solvent-free highsolids two-component coating compositions.

All parts and percentages in the examples which follow are by weight,unless otherwise indicated.

EXAMPLES Example 1

A round bottom flask was fitted with stirrer, heating mantle, nitrogeninlet, thermocouple and addition funnel. 140 grams (1.34 eq.)bis-(para-aminocyclohexyl)methane (PACM) was added to the flask at roomtemperature. 115 g (0.67 eq) diethyl maleate was added through theaddition funnel over a period of thirty minutes. The temperature of theflask rose to 35° C. The reaction was heated to 60° C. and held forseven hours at which time the IR spectrum indicated that the reactionwas 99% complete. The reaction mixture was cooled to room temperature.202 grams (1.34 eq) butyl glycidyl ether was added over a half hourperiod. The temperature was increased to 60° C. and held for twenty fourhours, when the primary-amine amine number was 160 (theory 164). Theproduct had a 25° C. viscosity of 2,700 mPa·s.

Examples 2, 3 and 4

Coatings were prepared at 100% solids by blending with Desmodur N-3300.(Desmodur N-3300 is a commercially available Bayer Polymers LLC trimerbased on hexane diisocyanate having an NCO content of about 22%, aviscosity at 25° C. of about 2500 mPa·s, and an NCO equivalent weight ofabout 193.) Resins were mixed with N3300 at an NCO/(OH—NH)=1.05.Materials were double stirred to insure proper mixing. The materials andamounts used were as indicated in the following table. PACM-basedhydroxy PACM/DEM aspartate from Example 1 diaspartate* Example 2 3 4Asparate from 277 g 277 g — Example 1 (1.0 eq) (1.0 eq) Comparisonaspart. — — 277 g (1.0 eq) Desmodur N-3300 205 g 205 g 205 g (1.05 eq)(1.05 eq) (1.05 eq) T-12, dibutyltin — 0.01 phr — dilaurate Work life30-45 min 3-4 min 15-20 min. Hard-dry times 6+ hours 0.5 hours 0.5 hoursHardness, Shore D Soft 42 82*the comparison material was the reaction product of one mole of PACMand 2 moles of diethylmaleate.

Work life end point was measured as the point the material had curedenough to lift cup easily with stir. Dry times were conducted in theconstant temperature-humidity room using a six hour meter for hard dry.Hardness was done after one day cure using a Shore D probe. A surprisewas the fast response of the hydroxy aspartate to catalysis. Normally,higher levels of tin catalysts are used to achieve this fast of a harddry time.

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

1. An aspartate of the formula:

where X represents an m-valent organic residue obtained by removing theprimary amino group or groups from a mono or polyamine which has(cyclo)aliphatically bound amino groups and a number average molecularweight of 60 to 6000, and which may contain further functional groupsthat either are reactive with isocyanate groups or are inert toisocyanate groups at temperatures of up to 100° C., R₁ and R₂ may beidentical or different and represent hydrogen or organic groups whichare inert towards isocyanate groups at a temperature of 100° C. or less,R₃ and R₄ may be identical or different and represent organic groupswhich are inert towards isocyanate groups at a temperature of 100° C. orless, R₅ represents hydrogen or together with R_(5′) and the carbonatoms to which they are connected forms a six-membered cycloalkyl group,with said cycloalkyl group being substituted with from 0 to 3 alkylgroups having from 1 to 3 carbon atoms, R_(5′) represents a moietyselected from the group consisting of i) C₁ to C₈ alkyl groups which maybe interrupted with an oxygen atom, ii) C₆ to C₁₀ aryl groups, which maybe substituted with up to three alkyl groups having from 1 to 3 carbonatoms and iii) C₆ to C₁₂ cycloalkyl groups, which may be substitutedwith up to three alkyl groups having from 1 to 3 carbon atoms, R₆represents hydrogen or together with R_(6′) and the carbon atoms towhich they are connected forms a six-membered cycloalkyl group, withsaid cycloalkyl group being substituted with from 0 to 3 alkyl groupshaving from 1 to 3 carbon atoms, R_(6′) represents a moiety selectedfrom the group consisting of i) C₁ to C₈ alkyl groups which may beinterrupted with an oxygen atom, ii) C₆ to C₁₀ aryl groups, which may besubstituted with up to three alkyl groups having from 1 to 3 carbonatoms and iii) C₆ to C₁₂ cycloalkyl groups, which may be substitutedwith up to three alkyl groups having from 1 to 3 carbon atoms, with theproviso that R₅ and R₆ are the same and R_(5′) and R_(6′) are the same,and a and b represent integers of from 1 to 5, provided that the sum ofa and b is from 2 to
 6. 2. A process for preparing an asparatate of theformula:

where X represents an m-valent organic residue obtained by removing theprimary amino group or groups from a mono or polyamine which has(cyclo)aliphatically bound amino groups and a number average molecularweight of 60 to 6000, and which may contain further functional groupsthat either are reactive with isocyanate groups or are inert toisocyanate groups at temperatures of up to 100° C., R₁ and R₂ may beidentical or different and represent hydrogen or organic groups whichare inert towards isocyanate groups at a temperature of 100° C. or less,R₃ and R₄ may be identical or different and represent organic groupswhich are inert towards isocyanate groups at a temperature of 100° C. orless, R₅ represents hydrogen or together with R_(5′) and the carbonatoms to which they are connected forms a six-membered cycloalkyl group,with said cycloalkyl group being substituted with from 0 to 3 alkylgroups having from 1 to 3 carbon atoms, R_(5′) represents a moietyselected from the group consisting of i) C₁ to C₈ alkyl groups which maybe interrupted with an oxygen atom, ii) C₆ to C₁₀ aryl groups, which maybe substituted with up to three alkyl groups having from 1 to 3 carbonatoms and iii) C₆ to C₁₂ cycloalkyl groups, which may be substitutedwith up to three alkyl groups having from 1 to 3 carbon atoms, R₆represents hydrogen or together with R_(6′) and the carbon atoms towhich they are connected forms a six-membered cycloalkyl group, withsaid cycloalkyl group being substituted with from 0 to 3 alkyl groupshaving from 1 to 3 carbon atoms, R_(6′) represents a moiety selectedfrom the group consisting of i) C₁ to C₈ alkyl groups which may beinterrupted with an oxygen atom, ii) C₆ to C₁₀ aryl groups, which may besubstituted with up to three alkyl groups having from 1 to 3 carbonatoms and iii) C₆ to C₁₂ cycloalkyl groups, which may be substitutedwith up to three alkyl groups having from 1 to 3 carbon atoms, with theproviso that R₅ and R₆ are the same and R_(5′) and R_(6′) are the same,and a and b represent integers of from 1 to 5, provided that the sum ofa and b is from 2 to 6, comprising A) reacting at a temperature of 0 to100° C., in solution or in the absence of a solvent and at an equivalentratio of primary amino groups in component a) to C═C double bonds incomponent b) of from about 1.1:1 to about 3.0:1 a) mono or polyaminescorresponding to formula (II)X[—NH₂]_(m)   (II)  with b) compounds corresponding to formula (III)R₃OOC—C(R₁)═C(R₂)—COOR₄   (III)  wherein X, R₁, R₂, R₃ and R₄ are asdefined above and m represents an integer of from 2 to 6, and B)reacting the resultant product with an oxirane compound selected fromthe group consisting of alkylene oxides, cycloalkylene oxides, andphenylglycidyl ether.
 3. A two-component coating composition whichcomprises, as binder, a) a polyisocyanate component and b) anisocyanate-reactive component containing b1) the aaspartate of claim 1.b2) optionally other isocyanate-reactive compounds, wherein theequivalent ratio of isocyanate groups to isocyanate-reactive groups isfrom about 0.8:1 to about 2.0:1.
 4. A prepolymer containing urea,urethane, allophanate and/or biuret structures comprising the reactionproduct of a polyisocyanate with the aspartate of claim 1.